1. Field of the Invention
The present invention relates to a semiconductor acceleration detecting device mounted with a semiconductor chip for detecting an acceleration.
2. Description of the Prior Art
Conventionally, as a semiconductor acceleration detecting device (referred to appropriately as an acceleration detecting device or simply as a device hereinafter), there has been a known device in which a package body formed by mounting an acceleration detecting semiconductor chip on a die pad and molding it with the lead terminal sections of lead pins protruding outward is combined by bonding with a main body section having an acceleration detecting mass body as totally formed into an approximately rectangular parallelepiped shape (including a cube). In this case, the acceleration detecting device is totally formed into an approximately rectangular parallelepiped shape comprised of a pair of first surfaces from which the lead terminal sections are protruding, a pair of second surfaces which are approximately parallel to the lead terminal sections and approximately perpendicular to the die pad and a pair of third surfaces which are approximately parallel to the die pad.
The acceleration detecting device as described above is normally used as assembled into a unit body having a specified electric circuit and connected electrically and mechanically to the unit body via the lead terminal sections.
In the above acceleration detecting device, as described later, the acceleration detecting mass body assembled into the main body section is cantilevered by a thin beam, and this mass body swings when an acceleration is effected in a specified direction.
Then, the magnitude of the swing (i.e., the magnitude of the acceleration) of this mass body is detected and outputted as an electric signal. For the purpose of increasing the quantity of swing of the mass body due to the effect of the acceleration and increasing the detection accuracy and sensitivity, the thickness of the beam which supports the mass body is set to a very thin thickness.
For the above reasons, if the acceleration detecting device is handled not properly, e.g., it is dropped when handled, particularly in an assembling stage into the unit body, or in a preceding conveyance stage, and consequently an impact load in excess of a certain degree is applied to the acceleration detecting device due to the drop or the like, the beam for supporting the aforementioned mass body may be damaged.
To solve the above problem, a cushioning material may be attached to each of the surfaces other than the first surfaces from which the lead terminal sections of the acceleration detecting device protrude. However, in this case, a separate cushioning material is necessary, and it takes much time and labor for attaching the material to each required surface, causing the additional problem of higher cost.
Assuming that the mass of the mass body is M and the movement velocity of the acceleration detecting device in the impact effecting stage is V, then an impact force F applied to the beam for supporting the mass body is expressed by the following equation (1) as a product obtained by multiplying the mass M of the mass body by an acceleration .DELTA.V/.DELTA.t (t: time). EQU F=M.multidot.(.DELTA.V/.DELTA.t) (1)
Therefore, in order to reduce the impact force F applied to the beam, it is required to reduce the mass M of the mass body or allow .DELTA.t to be increased by easing the impact. In this case, the mass M of the mass body cannot be reduced for the purpose of maintaining the detection accuracy and sensitivity of the acceleration detecting device. Therefore, the above matter must be managed by increasing .DELTA.t.
When the acceleration detecting device receives an impact due to the drop thereof or the like and this impact is received by the first surface from which the lead terminal section protrudes, the impact force F exerted on the beam is reduced since the impact is eased by the lead terminal section protruding from the surface (i.e., since .DELTA.t is increased).
However, since the other surfaces (second surface and third surface) are provided with nothing to ease the impact, a great impact force F is applied to the beam when the acceleration detecting device receives the impact by any of these surfaces. Therefore, these surfaces are also required to be provided with a cushioning member which protrudes from the surfaces and eases the impact.
In the case where the acceleration detecting device is dropped to collide with a floor surface or the like, the greatest impact force F is exerted on the beam when the acceleration detecting device two-dimensionally receives the drop impact and no rebound occurs when the device collides with the floor surface or the like (i.e., when the impact is received with one shock). In this case, the velocity V in the aforementioned equation (1) becomes zero in an extremely short time (.DELTA.t=0), when an intense impact force F is exerted on the beam.
However, when the acceleration detecting device once collides with the floor surface by, for example, a corner portion of the package, a rebound occurs and the device receives the impact in a plurality of times (i.e., with two or more shocks), meaning that .DELTA.t in the aforementioned equation (1) can be increased by that much for the improvement of the impact resistance.
Therefore, when the surfaces (second surfaces and third surfaces) other than the first surface from which the lead terminal section of the acceleration detecting device protrudes are provided with protruding members which protrude from the surfaces and ease the impact, there must be a protrusion configuration, for promoting the occurrence of rebound without any drop impact received two-dimensionally i.e. two or more points of simultaneous impact for surfaces and/or protrusions of the device.
The die pad to be mounted with an acceleration detecting semiconductor chip is supported by a lead frame normally via suspension leads which extend in the direction perpendicular to the lead pins. The suspension leads are cut from the lead frame after being molded with the lead terminal sections of the lead pins protruding outward, when the suspension leads are cut normally along the outer wall of the package body so that a remaining suspension lead which remains as connected to the die pad is not exposed outwardly of the package.
However, when the remaining suspension lead is cut along the frame of the lead frame, the remaining suspension lead protrudes from the outer wall of the package body, and this remaining suspension lead can be utilized for effecting a shock absorbing effect on the surface.
In regard to the matter of protruding the remaining suspension lead outwardly of the package body, several prior art constructions, which do not intend to make the remaining suspension lead produce the shock absorbing effect, are disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI 3-263862 (first prior art), Japanese Patent Laid-Open Publication No. HEI 4-130653 (second prior art) or Japanese Patent Laid-Open Publication No. HEI 8-32007 (third prior art), for the purpose of utilizing the remaining suspension lead as a power lead, as a means for improving the heat radiating performance of the package body or the like by exposing the remaining suspension lead from the outer wall of the package body.
Furthermore, since the main body section and the package body in which the acceleration detecting mass body is assembled is normally made of a resin material, and therefore, it is easy to provide a protrusion on a specified surface in the molding stage. It is possible to make such a protrusion produce the shock absorbing effect.
In regard to the provision of such a protrusion, a prior art construction, which do not intend to make the protrusion produce the shock absorbing effect, is disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI 3-125468 (fourth prior art) in which a protrusion for temporarily fixing the package body on a board is provided on one surface side of the package body.
However, the constructions disclosed in the aforementioned prior art have the following problems in terms of the improvement of the impact resistance performance.
That is, according to the first prior art, the remaining suspension lead is drawn out of the package body as a heat radiating lead frame. In this case, the remaining suspension lead is arranged in a planar configuration such that it fits along a specified surface of the package body. When the device collides with the floor surface or the like due to the drop thereof or the like, it tends to two-dimensionally receive the drop impact, and the occurrence of rebound due to the remaining suspension lead is scarcely expected. Therefore, it is difficult to surely make the device receive the impact in the dropping stage in a plurality of times (i.e., with more two or more shocks), meaning that the impact resistance cannot be sufficiently improved. Furthermore, according to this first prior art, the remaining suspension lead is set widely so as to cover almost the entire specified surface of the package body, where the lead frame is very specific.
Furthermore, according to the second prior art, the remaining suspension lead is utilized as a power lead. In this case, the surfaces parallel to the die pad of the package body are provided with no shock absorbing mechanisms, and the leading ends of a pair of wide remaining suspension leads are bent and formed flatly with their quantities of protrusion regulated. In the case where the device is dropped with the flat portion facing down, the device tends to two-dimensionally receive the drop impact when it collides with the floor surface or the like. Therefore, when the device is dropped like this, it is scarcely expected to surely generate a rebound by the remaining suspension lead.
Furthermore, according to the third prior art, the remaining suspension lead is protruding outwardly of the package body as a heat radiating lead pin. Also, in this case, the leading ends of the remaining suspension leads are bent and formed flatly with the quantities of protrusion of them regulated for the mounting to the assembly body. In the case where the device is dropped with the flat portion facing down, it also tends to two-dimensionally receive the drop impact when it collides with the floor surface or the like. Therefore, when the device is dropped like this, it is scarcely expected to surely generate a rebound by the remaining suspension lead.
Furthermore, according to the fourth prior art, the resin protrusion is formed only on one surface side of the package body, meaning that all the six surfaces of the rectangular parallelepiped are not provided with a shock absorbing mechanism. Furthermore, the quantities of protrusion of a pair of resin protrusions are regulated for the temporary fixation of them on a board, and the device tends to two-dimensionally receive a drop impact when it is dropped in the direction in which the protrusion extends.
Accordingly, the present invention has been developed with an object for providing a semiconductor acceleration detecting device capable of improving the impact resistance when it is handled singly with a relatively simple construction without providing any other member.